The UN has launched a diphtheria vaccination campaign in Yemen, for more than 2.8 million children aged from six weeks to 15 years.
UN spokesman Stephane Dujarric said on Thursday that more than 4,000 Yemenis developed diphtheria since 2017, and more than 200 had died.
Mr Dujarric said preliminary data from the World Health Organisation and Unicef indicated that more than a million children were vaccinated within the first five days of the campaign.
Diphtheria is an infectious and contagious disease that usually hits the nose, throat and air passages, but may also infect the skin.
Mr Dujarric said more than 8,000 health workers and community volunteers were taking part in the vaccination campaign in eight cities including Hodeidah, Al Jawf, Dhamar and Ibb.
More than 12 million children in Yemen are in need of aid and 360,000 of those under the age of five are severely malnourished, Unicef says.
This year, the UN agency appealed for $542 million (Dh1.99 billion) to continue responding to the needs of children in Yemen.
The UAE, which supports the Yemeni government, has pledged more than $4bn in aid over the past three years.